The present invention relates to retractable cord reel devices. In particular, the present invention relates to retractable cord reel devices of a small size suitable for use with hand held electronic devices such as cellular telephones and the like.
Retractable cord reel devices may be used to dispense and automatically recall cords that connect one component of an apparatus to another. The connection may be electronic, as in the case of a small cellular telephone, for instance, where a retractable cord reel may be used to connect a microphone and ear piece or headphone to the base telephone unit.
Most cord reels comprise a rotating spool on which a retractable cord is held. Some prior art devices provide rotating electrical contacts between the spool and the spool housing or base member. In electronic applications, particularly those involving low current signals, moving contacts can cause static and other undesirable signal disruptions. Further, contacts systems are not very durablexe2x80x94the quality of the electrical contact deteriorating with wear.
One solution to rotating contacts is to provide a second cable, typically flat, within the cord reel that expands and contracts as the retractable cord is retracted and returned. See, for example, U.S. Pat. No. 5,094,396 to Paul C. Burke. However, cord reels of this type may be too large for use with small electronic devices, such as cellular telephones. Specifically, the reel disclosed in the Burke ""396 patent has multiple compartments for the retractable cord, expandable cable, spring and ratchet. As a result the housing is relatively large, and would not be suitable for incorporation into a small electronic device such as a cell phone.
Also, many prior art designs do not adequately address the significant stress that is put on the moving parts of such small reels. As a telephone ear piece is pulled by hand from a telephone, a great deal of stress may result. Over repeated uses this stress often results in failure of an electrical connection or mechanical failures for the small gage cables (e.g., Litz wire) and other parts used in prior art reel devices. Larger, more durable cables are not practical because of the required small reel size, and because of the need for a lightweight, flexible cord for use with an earphone and/or microphone.
Also, many prior art cord reel devices suitable for use with small applications do not provide for adequate shielding of electrical signals from interference. This problem is particularly acute for small telephones and the like using a microphone and earphone of a very low voltage. Inadequate shielding results in cross talk and other electronic noise. The small gage cables, small cable reels, and small cable housings of many prior art designs sacrifice adequate shielding for compact size.
There is therefore an unresolved need for a cord reel device that is compatible with the particular challenges presented by use with small electronic devices such as cellular phones and the like.
It is an object of the invention to provide a cord reel device of a compact design.
It is a further object of the invention to provide a durable cord reel device having improved resistance to stress related fatigue failures.
It is a still further object of the invention to provide a cord reel device having effective shielding to electrical interference.
The retractable cord reel of the present invention generally comprises a housing or base plate supporting an arbor, a spool rotatably mounted on the arbor, a retractable cord held on the spool, and a device for rotating the spool to retract the cord. The spool has an annular wall which defines an inner chamber and an outer trough. The retractable cord is held within the spool outer trough. A first end of the retractable cord is adjacent to the annular wall, and the other end retractably extends outwardly from the spool. The retraction device preferably comprises a spring that is helically wound in the spool inner chamber. An inner cable is also contained in the spool inner chamber, helically wound with the spring. The inner cable has one end conductively connected to the retractable cord, and a second end is stationary at the center of the spool.
A preferred embodiment of the present invention is useful to connect a cellular telephone base unit or source to a remote device such as a ear piece and microphone. In this embodiment, the telephone base unit provides a housing for the cord reel of the invention. The arbor is mounted to the housing or on a base plate contained within the housing. The spool is rotatably mounted on the arbor. The housing includes a radial opening through which an end of the retractable cord can pass. A ratchet mechanism may also be held in the housing or base plate to selectively restrain rotation of the spool. Although desirable, a ratchet is not strictly required.
The retractable cord comprises a plurality of conductors, at least one of the conductors, e.g., the mic conductor, is surrounded by an electromagnetic shield. The plural conductors are in turn covered by a reinforcing fabric layer. The reinforced fabric, preferably nylon braid, is mechanically attached to the spool, thereby providing a secure attachment that relieves the inner conductors from mechanical stress. A small gage conductor, such as Litz wire, can therefore be used without undue risk of failure. Accordingly, the retractable cord has desirable qualities including a small diameter, good flexibility, light weight, and good tensile strength.
The spring is preferably connected at a first end to the arbor, and at a second end to the spool, such as the annular wall separating the inner chamber from the outer trough. The spring is wound so that it builds and stores energy when the retractable cord is retracted from the spool. Upon release of the cord, the spring rotates the spool in a cord retracting direction.
An inner cable is helically wound with the spring in the inner chamber of the preferred cord reel embodiment of the invention. The preferred inner cable comprises one or more conductors electrically connecting a source, such as the telephone base unit, to the conductors of the retractable cord. The source is directly connected to the retractable cord, thereby avoiding intermittent disruption of signal that may result from moving contacts as utilized in the prior art. Winding the inner cable with the spring eliminates the need for a separate chamber or other additional space. The inner cable may comprise a flat ribbon cable, a strip conductor, individual conductors, or other configurations. The inner cable may be attached to the spring, or it may be separately wound with the spring. In any event, the conductors of the inner cable are insulated from the spring.
A preferred inner cable comprises a plurality of conductors carried on the spring having insulating layer(s) between the spring and the conductors. The inner cable conductors preferably comprise thin conductive strips, such as metal strips. The conductive strips may be thin metal foils, or can be formed by painting or printing conductive material onto a plastic or other insulating layer. The sub-assembly of the conductors, insulating layers and spring may be constructed in several ways. For example, plural, spaced apart, conductive strips may be sandwiched between two layers of an insulating material, such as mylar, and then adhered to the spring. An alternative construction comprises, a layer of insulating material adhered to the spring, plural spaced conductors adhered over the insulating layer, and an insulating coating applied over the top of the conductors. A third example comprises a layer of insulating material adhered to the spring, plural spaced conductors adhered over the insulating layer, and an insulating coating applied to the bottom surface of the spring. Other ways of insulating the conductors from the spring will be apparent to persons skilled in the art.
The spool and/or the housing and base plate of the preferred cord reel embodiment of the invention is shielded. The shield is preferably a nickel plating or coating, providing an electromagnetic/radio frequency interference (xe2x80x9cEMI-RFIxe2x80x9d) shield. As described above, the retractable cord likewise has a shielding layer around at least one conductor. The inner cable, however, is not required to have individual shielding as it is contained in the inner chamber and thus shielded by the metal spring, and the plating layers of the spool walls and/or the housing and base plate.
The overall result of the space savings realized by the compact retractable cord, the inner cable, and other compact elements of the configuration of the spool of the invention allow for a most advantageous compact spool size. The preferred spool has a diameter of less than 4 cm (1xc2xd inch), and a thickness of less than about 2 cm (xc2xe inch), and most preferably less than 1 cm (xe2x85x9c inch).
The above brief description sets forth rather broadly the more important features of the present disclosure so that the detailed description that follows may be better understood, and so that the present contributions to the art may be better appreciated. There are, of course, additional features of the disclosure that will be described hereinafter which will form the subject matter of the claims appended hereto. In this respect, before explaining the several embodiments of the disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and the arrangements set forth in the following description or illustrated in the drawings. The present invention is capable of other embodiments and of being practiced and carried out in various ways, as will be appreciated by those skilled in the art. Also, it is to be understood that the phraseology and terminology employed herein are for description and not limitation.